For as long as humans have been farming, they’ve been trying to figure out what’s going on below ground. Soil is incredibly complex—full of organisms, microbes and chemicals that move and change constantly—and it all feeds into crop health and the Earth’s nutrient cycles in ways that aren’t fully understood. But getting data was a problem, since this generally required taking soil samples and then analyzing them in the lab, which is slow and often expensive.Recent advances in wireless data communications and the growing revolution of portable, cheap sensors have made it possible for UChicago scientists, including Profs. Monisha Ghosh and Supratik Guha, both affiliated with the Institute for Molecular Engineering, to start a pilot program to take real-time soil measurements—and they started in their own campus.

Their project, called the Thoreau sensor network, buried more than 30 sensing boxes in a variety of different locations around the UChicago campus. Each one is a cube about five inches square, containing four sensors that measure the soil’s water content, salt, temperature and water potential, the measure of how readily the soil holds or drains moisture. Twice an hour, a tiny radio transmitter and antenna—fully buried underground—sends a burst of data to the receiver, located atop the William Eckhardt Research Center.

For the hardware, they used commercial sensors that already exist. But there were a lot of questions about how the sensors might behave underground: Can the signals make it to the receivers above ground? Does the battery die faster? What happens to the machinery during freeze-thaw cycles?

“This test run provides us extremely helpful real-world data on how one could actually run a sensor network like this,” Ghosh said. “For example, the Chicago winter gave us some very helpful information.” (A few of the sensors didn’t survive last winter.)